1. Field of the Invention
The invention relates to electric motors, in particular a commutator motor.
2. Description of the Prior Art
Electric motors of the type with which this invention is concerned are used for example in motor vehicles as drive motors for window controls, sliding roof actuators, seat adjusters, mirror adjusters, and the like, and make it possible to establish predetermined setting positions with high precision. Scanning of the revolution and/or rpm is done by means of a Hall sensor disposed in a fixed fashion, which detects the magnetic pulses output by the two- or multi-pole ring magnet upon each revolution.
In a prior art motor of this type known from German Patent Disclosure DE 197 10 015 A1, the carrier ring is made of plastic; toward one face end, it has a conical tapering, and toward the other end it has a wedge-shaped recess. On the side of the wedge-shaped recess, a two-pole ring magnet is injection molded on, and the wedge-shaped recess brings about a good connection between the ring magnet and the carrier ring. The carrier ring is slipped with a press fit onto the rotor shaft, which facilitates assembly and makes it possible to dispense with glue for fixation purposes. The press fit is selected such that it absorbs the requisite tangential and axial forces. Producing the carrier ring of plastic makes the press fit possible without rupture of the ring magnet by mechanical stresses, since the soft plastic absorbs the stresses generated by the pressing. The conical shape of the carrier ring at the front serves to push the commutator brushes apart during assembly, so that a separate auxiliary tool for spreading the commutator brushes apart so that the magnet body seated on the rotor shaft can be pushed through can be dispensed with, thus facilitating the assembly. Once the motor is mounted in its final position, the carrier ring with the ring magnet is positioned on the rotor shaft directly upstream of the commutator brushes and downstream of a shaft bearing structurally connected to the housing, and with its face end it supports the rotor shaft axially on the shaft bearing, as long as no gear has yet been connected to the motor.
The electric motor of the invention has the advantage that the ring magnet is received by the carrier ring outside of the press fit of the carrier ring, and as a result, the stresses generated by the press fit cannot reach the fragile ring magnet, and especially not if, in a preferred embodiment of the invention, the region of the second annular portion is embodied in slit form. It is thus possible to embody the carrier ring as a metal or sintered ring, which allows a press fit with high force transmission to the rotor shaft, which is desirable for high-speed electric motors. Moreover, a metal ring is highly suitable for running up against a rotor shaft sintered bearing structurally connected to the housing. Even varying temperature conditions do not lead to stresses that threaten the ring magnet in the second annular portion of the carrier ring.
In a preferred embodiment of the invention, the outer jacket of the second annular portion that receives the ring magnet is provided with pinecone-like axial, radial or intersecting ribs. This ribbing assures an adequately firm seat of the ring magnet on the carrier ring. A ring magnet made of plastoferrite digs into this ribbing by relaxation.
In an advantageous embodiment of the invention, the carrier ring is made of nonmagnetic material, so that a loss of flux by a short circuit in the first annular portion is averted.
In an advantageous embodiment of the invention, the carrier ring is produced from a material with slip, such as red bronze or brass. Because of the good slip of the carrier ring, the usual plastic stop disk can be omitted, and the carrier ring can run directly up against the shaft bearing. When the motor is put together, the longitudinal play of the rotor or armature shaft is adjusted, by overpressing a plastic bearing plate that receives the shaft bearing, to the minimum amount that is required by different thermal expansions.